Unveiling the Role of Adsorbent–Catalyst Proximity in Integrated CO ₂ Capture and Dry Reforming of Methane over Ni-CaO/CeO ₂ Systems

Integrated CO 2 capture and utilization via dry reforming of methane (ICCU-DRM) using Ni-CaO dual-function materials (DFMs) is a promising route for simultaneous CO 2 mitigation and syngas production. However, the rational design of durable DFMs requires a fundamental understanding of how adsorption-catalytic site proximity governs performance and stability. We establish a proximity gradient spanning 3 orders of magnitude, from millimeter scale (separated beds) through micrometer scale (physical mixture) to nanometer scale (monolithic DFMs), to demonstrate proximity effects on ICCU-DRM using distinct Ni-CaO/CeO 2 configurations. The monolithic Ni-CaO/CeO 2 -DFMs with maximized interfacial contact achieve the highest CO 2 capture capacity (12.0 mmol CO 2 /g) and syngas yield (10.7 mmol CO/g and 20.9 mmol H 2 /g), with robust durability over 20 cycles (5% decay in syngas yield with a rate of ∼0.05 mmol/g/cycle) despite observable carbon deposition. In situ diffuse reflection infrared Fourier transform spectroscopy (DRIFTS) analysis reveals that the intimate architecture of the monolithic DFMs facilitates a direct reaction pathway via hydrogen-spillover-driven intermediates at the Ni-CaO interface. In contrast, the physical mixture configuration (Ni-CaO/CeO 2 –Phy) follows a diffusion-limited, gas-phase-mediated route, resulting in lower initial activity but exceptional cyclic stability (<2% decay in syngas yield) and negligible coking. Separated-bed configurations suffer rapid deactivation either from sintering and coking with adsorbent upstream (Ni-CaO/CeO 2 -D) or from intrinsically poor CH 4 conversion with catalyst upstream (Ni-CaO/CeO 2 -A). These findings demonstrate that proximity fundamentally governs the trade-off between high reactivity and long-term durability. Optimal DFM design requires integration at the correct length scale, providing critical guidance for engineering robust Ni-CaO DFMs with efficient CO 2 /CH 4 conversion and stability in ICCU-DRM.